V1/man/man1/sh.1
11/3/71 SH (I)
NAME sh -- shell (command interpreter)
SYNOPSIS sh [ name [ arg1 ... [ arg9 ] ] ]
DESCRIPTION sh is the standard command interpreter. It is the program
which reads and arranges the execution of the command lines
typed by most users. It may itself be called as a command
to interpret files of command lines. Before discussing the
arguments to the shell used as a command, the structure of
command lines themselves will be given.
Command lines are sequences of commands separated by
command delimiters. Each command is a sequence of non--blank
command arguments separated by blanks. The first argument
specifies the name of a command to be executed. Except for
certain types of special arguments discussed below, the
arguments other than the command name are simply passed to
the invoked command.
If the first argument represents the path name of an
executable file, it is invoked; otherwise the string
"/bin/" is prepended to the argument. (In this way the
standard commands, which reside in "/bin," are found.) If
this search too fails a diagnostic is printed.
The remaining non--special arguments are simply passed to
the command without further interpretation by the shell.
There are three command delimiters: the new line, ";" , and
"&". The semicolon ";" specifies sequential execution of
the commands so separated; that is,
coma; comb
causes the execution first of command coma, then of comb.
The ampersand "&" causes simultaneous execution:
coma & comb
causes coma to be called, followed immediately by comb
without waiting for coma to finish. Thus coma and comb
execute simultaneously. As a special case,
coma &
causes coma to be executed and the shell immediately to
request another command without waiting for coma.
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Two characters cause the immediately following string to be
interpreted as a special argument to the shell itself, not
passed to the command. An argument of the form <arg causes
the file arg to be used as the standard input file of the
given command; an argument of the form ">arg" causes file
"arg" to be used as the standard output file for the given
command.
If any argument contains either of the characters "?" or
"*" , it is treated specially as follows. The current
directory is searched for files which match the given
argument. The character "*" in an argument matches any
string of characters in a file name (including the null
string); ? matches any single character in a file name.
Other argument characters match only the same character in
the file name. For example, "*" matches all file names; "?"
matches all one--character file names; "ab*.s" matches all
file names beginning with "ab" and ending with ".s".
If the argument with "*" or "?" also contains a "/", a
slightly different procedure is used: instead of the
current directory, the directory used is the one obtained
by taking the argument up to the last "/" before a "*" or
"?". The matching process matches the remainder of the
argument after this "/" against the files in the derived
directory. For example:, "/usr/dmr/a*.s" matches all files
in directory /usr/dmr which begin with "a" and end with
".s"
In any event, a list of names is obtained which match the
argument. This list is sorted into alphabetical order, and
the resulting sequence of arguments replaces the single
argument containing the "*" or "?". The same process is
carried out for each argument with a * or ?" (the resulting
lists are not merged) and finally the command is called
with the resulting list of arguments..
For example: directory /usr/dmr contains the files al * s,
a2.s, ..., a9.s. From any directory, the command
as /usr/dmr/a?.s
calls as with arguments /usr/dmr/al.s, /usr/dmr/a2.s, ...
/usr/dmr/a9.s in that order.
The character "\" causes the immediately following
character to lose any special meaning it may have to the
shell; in this way < , , and other characters meaningful to
the shell may be passed as part of arguments. A special
case of
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this feature allows the continuation of commands onto more
than one line: a new--line preceded by "\" is translated
into a blank.
Sequences of characters enclosed in double (") or single
(') quotes are also taken literally.
When the shell is invoked as a command, it has additional
string processing capabilities. Recall that the form in
which the whell is invoked is
sh [ name [ arg1 ... [ arg9 ] ] ]
The name is the name of a file which will be read and
interpreted. If not given, this subinstance of the shell
will continue to read the standard input file.
In the file, character sequences of the form "$n", where n
is a digit 0, ..., 9, are replaced by the nth argument to
the invocation of the shell (arg ). $0" is replaced by
name.
An end--of--file in the shell's input causes it to exit. A
side effect of this fact means that the way to log out from
UNIX is to type an end of file.
FILES /etc/glob
SEE ALSO [reference], which gives the theory of operation of the
shell.
DIAGNOSTICS "?", in case of any difficulty. The most common problem is
inability to find the given command. Others: input file
("<") cannot be found; no more processes can be created
(this will alleviate itself with the passage of time). Note
that no diagnostic is given for inability to create an
output (">") file; the standard output file has already
been closed when the condition is discovered and there is
no place to write the diagnostic.
If a "*" or "?" is used, the "glob" routine is invoked; it
types "No command" if it cannot find the given command, and
"No match" if there were no files which matched an argument
with "?" or "*".
BUGS Better diagnostics should be provided. If a "*" or "?" is
used, the command must be in /bin (Not, for example, in the
user's directory.) This is actually a glob bug.
OWNER dmr, ken